The described invention relates in general to seals and sealing assemblies, systems, devices, and methods, and more specifically to an agitator shaft seal assembly for use with large-scale industrial mixers such as the horizontal mixers that are used for processing bread and cookie dough.
Industrial mixers and blenders are typically used to mix or blend a wide range of materials used in different industries including the food, chemical, pharmaceutical, plastic and mineral industries. Mixers are machines that blend, homogenize, emulsify or otherwise mix materials and substances into a single substance by thoroughly combining virtually any solid or liquid that is necessary to form a final product. Specific examples of industrial mixers include dry blending devices, paste mixing designs for high viscosity products, and high shear models for emulsification, particle size reduction and homogenization. Industrial mixers range from laboratory to production line scale, and though mixers vary by size and design, the majority of these devices include large tanks, vats, or mixing bowls in which motorized blades or paddles rotate on or around one or more agitator shafts. Mixers are commonly constructed from stainless steel due to the desirable sanitary and corrosion-resistant properties of this metal, although other materials such as thermoplastics, titanium, cast iron, or aluminum may be used.
Because industrial mixers, when in use, often contain substances that must not be contaminated or lost during processing, various seals or sealing assemblies are included on certain components of these mixers. Of particular importance are the seals mounted on the exterior of the mixing reservoir or bowl around the ends of agitator shafts that protrude through walls of the mixing reservoir or bowl. Two commonly used seals of this nature include radial shaft seals (also referred to as “lip seals”) and rotary seals. Radial shaft seals are used to seal rotary elements, such as a shaft or rotating bore, and generally include a rubber or elastomeric sealing lip, a metal case, and a garter spring. Rotary seals are designed in the form of a ring and are fitted between machine parts in relative rotation.
With regard to their use on industrial-scale horizontal mixers that are used for processing bread, cookie dough, and other materials and substances, both radial shaft seals and rotary seals suffer from significant limitations. For example, lips seal used on agitator shafts are known to wear grooves into the shafts over time, eventually necessitating replacement of the agitator shafts. Lip seals used on agitator shafts are also difficult to disassemble and clean and include small springs that may come loose and contaminate the product being mixed. Lip seals are also known to leak dough and water. Rotary seals used on agitator shafts are also difficult to disassemble and clean because they are mechanically complex and include numerous individual parts that must be removed, cleaned, and replaced. Rotary seals are difficult to reassemble in a manner that will consistently provide positive sealing, and if such seals are reassembled incorrectly, the seals may overheat and sustain damage. Rotary seals are also designed and sold for a variety of machines, most of which do not require the level of sanitation needed for dough mixers. Some rotary seals rely on compressed air to maintain the seal, and compressed air is a possible source of product contamination. Air also leaks out of the seals, wasting energy. Finally, most rotary seals have an enclosed cavity that can collect leaked dough, but cannot be visually inspected for contamination without taking the seal apart. Accordingly, there is an ongoing need for a more effective and loss problematic seal and/or seal assembly that can be used with horizontal dough mixers and other industrial mixers.